Systems and methods for wireless communication in sub gigahertz bands

ABSTRACT

Systems, methods, and devices for wireless communication. In one aspect, an apparatus for wireless communication is provided. The apparatus includes a receiver configured to receive a wireless signal comprising a packet. At least a portion of the wireless signal is configured to be received over a bandwidth lower than or equal to 1.25 MHz. The packet is formed from at least one orthogonal frequency-division multiplexing (OFDM) symbol comprising thirty-two tones. The thirty-two tones correspond to frequency subcarriers within the bandwidth. The thirty-two tones of the at least one OFDM symbol are allocated as: twenty-four data tones, two pilot tones, five guard tones, and one direct current (DC) tone. The apparatus includes a processor configured to evaluate the wireless signal. The processor includes a transform module configured to convert the at least one OFDM symbol into a frequency domain signal using a thirty-two point mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/875,638, filed on May 2, 2013 which is a continuation of U.S. patentapplication Ser. No. 13/410,633, filed on Mar. 2, 2012 which claimspriority and benefit under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication No. 61/449,582 entitled “SYSTEMS AND METHODS FOR WIRELESSCOMMUNICATION IN SUB-GIGAHERTZ BANDS” filed on Mar. 4, 2011, thedisclosure of which is hereby incorporated by reference in its entirety.U.S. patent application Ser. No. 13/410,633 additionally claims benefitunder 35 U.S.C. §119(e) to U.S. Provisional Patent Application No.61/471,173 entitled “SYSTEMS AND METHODS FOR SIGNALING IN A WIRELESSNETWORK” filed on Apr. 3, 2011, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

Field

The present application relates generally to wireless communications,and more specifically to systems, methods, and devices to enablewireless communication in sub-gigahertz bands. Certain aspects hereinrelate to orthogonal frequency-division multiplexing (OFDM)communications that are sent using 32 tones over a bandwidth of equal toor less than 1.25 MHz.

Background

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks may be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g., circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g., wired vs.wireless), and the set of communication protocols used (e.g., Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infra-red, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

The devices in a wireless network may transmit/receive informationbetween each other. The information may comprise packets, which in someaspects may be referred to as data units. The packets may includeoverhead information (e.g., header information, packet properties, etc.)that helps in routing the packet through the network, identifying thedata in the packet, processing the packet, etc., as well as data, forexample user data, multimedia content, etc. as might be carried in apayload of the packet.

SUMMARY

The systems, methods, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this invention provide advantages that include providingwireless communication in sub-gigahertz bands for low power and longdistance wireless communications.

One aspect of the disclosure provides a wireless communicationsapparatus. The apparatus includes a receiver configured to receive awireless signal including a packet. At least a portion of the wirelesssignal is received over a bandwidth lower than or equal to 1.25 MHz. Thepacket is formed from at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones. The thirty-twotones correspond to frequency subcarriers within the bandwidth. Thethirty-two tones of the at least one OFDM symbol are allocated as:twenty-four data tones, two pilot tones, five guard tones, and onedirect current (DC) tone. The apparatus includes a processor configuredto evaluate the wireless signal. The processor includes a transformmodule configured to convert the at least one OFDM symbol into afrequency domain signal using a thirty-two point mode.

Another aspect of the disclosure provides an implementation of a methodfor wireless communication. The method includes receiving a wirelesssignal including a packet, at least a portion of the wireless signalbeing received over a bandwidth lower than or equal to 1.25 MHz. Thepacket is formed from at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers within the bandwidth. Thethirty-two tones of the at least one OFDM symbol are allocated as:twenty-four data tones, two pilot tones, five guard tones, and onedirect current (DC) tone. The method further includes evaluating thewireless signal, the evaluating including converting the at least oneOFDM symbol into a frequency domain signal using a thirty-two pointmode.

Yet another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for receiving a wirelesssignal including a packet, at least a portion of the wireless signalbeing received over a bandwidth lower than or equal to 1.25 MHz. Thepacket is formed from at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers within the bandwidth. Thethirty-two tones of the at least one OFDM symbol are allocated as:twenty-four data tones, two pilot tones, five guard tones, and onedirect current (DC) tone. The apparatus further includes means forevaluating the wireless signal, the means for evaluating furtherincluding means for converting the at least one OFDM symbol into afrequency domain signal using a thirty-two point mode.

Another aspect of the disclosure provides a computer program product.The computer program product includes a computer readable medium. Thecomputer readable medium includes code for receiving a wireless signalincluding a packet, at least a portion of the wireless signal beingreceived over a bandwidth lower than or equal to 1.25 MHz. The packet isformed from at least one orthogonal frequency-division multiplexing(OFDM) symbol including thirty-two tones, the thirty-two tonescorresponding to frequency subcarriers within the bandwidth. Thethirty-two tones of the at least one OFDM symbol are allocated as:twenty-four data tones, two pilot tones, five guard tones, and onedirect current (DC) tone. The computer readable medium further includescode for evaluating the wireless signal, the code for evaluatingincluding code for converting the at least one OFDM symbol into afrequency domain signal using a thirty-two point mode.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes a processor configured to generatea packet for transmission via a wireless signal. The packet is generatedfor transmission using at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers. The thirty-two tones ofthe at least one OFDM symbol are allocated as: twenty-four data tones,two pilot tones, five guard tones, and one direct current (DC) tone. Theapparatus further includes a transform module configured to convert theat least one OFDM symbol into a time domain signal using a thirty-twopoint mode. The apparatus further includes a transmitter configured totransmit the packet via the wireless signal over a bandwidth that islower than or equal to 1.25 MHz.

Another aspect of the disclosure provides an implementation of a methodfor wireless communication. The method includes generating a packet fortransmission via a wireless signal. The packet is generated fortransmission using at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers. The thirty-two tones ofthe at least one OFDM symbol are allocated as: twenty-four data tones,two pilot tones, five guard tones, and one direct current (DC) tone. Themethod further includes converting the at least one OFDM symbol into atime domain signal using a thirty-two point mode. The method furtherincludes transmitting the packet via the wireless signal over abandwidth that is lower than or equal to 1.25 MHz.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes means for generating a packet fortransmission via a wireless signal. The packet is generated fortransmission using at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers. The thirty-two tones ofthe at least one OFDM symbol are allocated as: twenty-four data tones,two pilot tones, five guard tones, and one direct current (DC) tone. Theapparatus further includes means for converting the at least one OFDMsymbol into a time domain signal using a thirty-two point mode. Theapparatus further includes means for transmitting the packet via thewireless signal over a bandwidth that is lower than or equal to 1.25MHz.

Another aspect of the disclosure provides a computer program product.The computer program product includes a computer readable medium. Thecomputer readable medium includes code for generating a packet fortransmission via a wireless signal. The packet is generated fortransmission using at least one orthogonal frequency-divisionmultiplexing (OFDM) symbol including thirty-two tones, the thirty-twotones corresponding to frequency subcarriers. The thirty-two tones ofthe at least one OFDM symbol are allocated as: twenty-four data tones,two pilot tones, five guard tones, and one direct current (DC) tone. Thecomputer readable medium further includes code for converting the atleast one OFDM symbol into a time domain signal using a thirty-two pointmode. The computer readable medium further includes code fortransmitting the packet via the wireless signal over a bandwidth that islower than or equal to 1.25 MHz.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wireless communication system inwhich aspects of the present disclosure may be employed.

FIG. 2 shows a functional block diagram of an exemplary wireless devicethat may be employed within the wireless communication system of FIG. 1.

FIG. 3 shows a functional block diagram of exemplary components that maybe utilized in the wireless device of FIG. 2 to transmit wirelesscommunications.

FIG. 4 shows a functional block diagram of exemplary components that maybe utilized in the wireless device of FIG. 2 to receive wirelesscommunications.

FIG. 5 is a functional block diagram of an exemplary MIMO system thatmay be implemented in wireless devices such as the wireless device ofFIG. 2 to transmit wireless communications.

FIG. 6 is a functional block diagram of an exemplary MIMO system thatmay be implemented in wireless devices such as the wireless device ofFIG. 2 to receive wireless communications.

FIG. 7 is a block diagram showing an exemplary structure of a preambleand payload of a physical layer packet.

FIG. 8A is a block diagram showing an exemplary structure of a preambleand payload of a physical layer packet for transmission over a bandwidthof substantially 1 MHz.

FIG. 8B is a block diagram showing an exemplary structure of a preambleand payload of a physical layer packet for transmission over a bandwidthof substantially 2 MHz according to a single user mode.

FIG. 8C is a block diagram showing an exemplary structure of a preambleand payload of a physical layer packet for transmission over a bandwidthof substantially 2 MHz according to a multi user mode.

FIG. 9 is a block diagram shown another exemplary structure of apreamble and payload of a physical layer packet for transmission viawireless signal.

FIG. 10 is a block diagram shown another exemplary structure of apreamble and payload of a physical layer packet for transmission viawireless signal.

FIG. 11 is a block diagram shown another exemplary structure of apreamble and payload of a physical layer packet for transmission viawireless signal.

FIG. 12 is a block diagram shown another exemplary structure of apreamble and payload of a physical layer packet for transmission via awireless signal.

FIG. 13 is a flow chart of an exemplary method for receiving anddetermining a duration of a packet sent via a wireless signal.

FIG. 14 is a flow chart of an exemplary method for generating andtransmitting a packet via a wireless signal.

FIG. 15 is a flow chart of another exemplary method for receiving andevaluating a packet sent via a wireless signal.

FIG. 16 is a flow chart of another exemplary method for generating andtransmitting a packet via a wireless signal.

FIG. 17 is a functional block diagram of another exemplary wirelessdevice that may be employed within the wireless communication system ofFIG. 1.

FIG. 18 is a functional block diagram of yet another exemplary wirelessdevice that may be employed within the wireless communication system ofFIG. 1.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as WiFi or, more generally, any member of the IEEE 802.11family of wireless protocols. For example, the various aspects describedherein may be used as part of the IEEE 802.11ah protocol, which usessub-1 GHz bands.

In some aspects, wireless signals in a sub-gigahertz band may betransmitted according to the 802.11ah protocol using orthogonalfrequency-division multiplexing (OFDM), direct-sequence spread spectrum(DSSS) communications, a combination of OFDM and DSSS communications, orother schemes. Implementations of the 802.11ah protocol may be used forsensors, metering, and smart grid networks. Advantageously, aspects ofcertain devices implementing the 802.11ah protocol may consume lesspower than devices implementing other wireless protocols, and/or may beused to transmit wireless signals across a relatively long range, forexample about one kilometer or longer.

In some implementations, a WLAN includes various devices which are thecomponents that access the wireless network. For example, there may betwo types of devices: access points (“APs”) and clients (also referredto as stations, or “STAs”). In general, an AP serves as a hub or basestation for the WLAN and an STA serves as a user of the WLAN. Forexample, a STA may be a laptop computer, a personal digital assistant(PDA), a mobile phone, etc. In an example, an STA connects to an AP viaa WiFi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wirelesslink to obtain general connectivity to the Internet or to other widearea networks. In some implementations an STA may also be used as an AP.

An access point (“AP”) may also comprise, be implemented as, or known asa NodeB, Radio Network Controller (“RNC”), eNodeB, Base StationController (“BSC”), Base Transceiver Station (“BTS”), Base Station(“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, orsome other terminology.

A station “STA” may also comprise, be implemented as, or known as anaccess terminal (“AT”), a subscriber station, a subscriber unit, amobile station, a remote station, a remote terminal, a user terminal, auser agent, a user device, user equipment, or some other terminology. Insome implementations an access terminal may comprise a cellulartelephone, a cordless telephone, a Session Initiation Protocol (“SIP”)phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smartphone), acomputer (e.g., a laptop), a portable communication device, a headset, aportable computing device (e.g., a personal data assistant), anentertainment device (e.g., a music or video device, or a satelliteradio), a gaming device or system, a global positioning system device,or any other suitable device that is configured to communicate via awireless medium.

As discussed above, certain of the devices described herein mayimplement the 802.11ah standard, for example. Such devices, whether usedas an STA or AP or other device, may be used for smart metering or in asmart grid network. Such devices may provide sensor applications or beused in home automation. The devices may instead or in addition be usedin a healthcare context, for example for personal healthcare. They mayalso be used for surveillance, to enable extended-range Internetconnectivity (e.g., for use with hotspots), or to implementmachine-to-machine communications.

Certain of the devices described herein may further implement MultipleInput Multiple Output (MIMO) technology and be implemented as part ofthe 802.11ah standard. A MIMO system employs multiple (N_(T)) transmitantennas and multiple (N_(R)) receive antennas for data transmission. AMIMO channel formed by the N_(T) transmit and N_(R) receive antennas maybe decomposed into N_(S) independent channels, which are also referredto as spatial channels or streams, where N_(S)≦min{N_(T), N_(R)}. Eachof the N_(S) independent channels corresponds to a dimension. The MIMOsystem can provide improved performance (e.g., higher throughput and/orgreater reliability) if the additional dimensionalities created by themultiple transmit and receive antennas are utilized.

FIG. 1 illustrates an example of a wireless communication system 100 inwhich aspects of the present disclosure may be employed. The wirelesscommunication system 100 may operate pursuant to a wireless standard,for example the 802.11ah standard. The wireless communication system 100may include an AP 104, which communicates with STAs 106.

A variety of processes and methods may be used for transmissions in thewireless communication system 100 between the AP 104 and the STAs 106.For example, signals may be sent and received between the AP 104 and theSTAs 106 in accordance with OFDM/OFDMA techniques. If this is the case,the wireless communication system 100 may be referred to as anOFDM/OFDMA system. Alternatively, signals may be sent and receivedbetween the AP 104 and the STAs 106 in accordance with CDMA techniques.If this is the case, the wireless communication system 100 may bereferred to as a CDMA system.

A communication link that facilitates transmission from the AP 104 toone or more of the STAs 106 may be referred to as a downlink (DL) 108,and a communication link that facilitates transmission from one or moreof the STAs 106 to the AP 104 may be referred to as an uplink (UL) 110.Alternatively, a downlink 108 may be referred to as a forward link or aforward channel, and an uplink 110 may be referred to as a reverse linkor a reverse channel.

The AP 104 may act as a base station and provide wireless communicationcoverage in a basic service area (BSA) 102. The AP 104 along with theSTAs 106 associated with the AP 104 and that use the AP 104 forcommunication may be referred to as a basic service set (BSS). It shouldbe noted that the wireless communication system 100 may not have acentral AP 104, but rather may function as a peer-to-peer networkbetween the STAs 106. Accordingly, the functions of the AP 104 describedherein may alternatively be performed by one or more of the STAs 106.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice 202 that may be employed within the wireless communication system100. The wireless device 202 is an example of a device that may beconfigured to implement the various methods described herein. Forexample, the wireless device 202 may comprise the AP 104 or one of theSTAs 106.

The wireless device 202 may include a processor 204 which controlsoperation of the wireless device 202. The processor 204 may also bereferred to as a central processing unit (CPU). Memory 206, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 204. A portion of thememory 206 may also include non-volatile random access memory (NVRAM).The processor 204 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206. Theinstructions in the memory 206 may be executable to implement themethods described herein.

The processor 204 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 202 may also include a housing 208 that may includea transmitter 210 and a receiver 212 to allow transmission and receptionof data between the wireless device 202 and a remote location. Thetransmitter 210 and receiver 212 may be combined into a transceiver 214.An antenna 216 may be attached to the housing 208 and electricallycoupled to the transceiver 214. The wireless device 202 may also include(not shown) multiple transmitters, multiple receivers, multipletransceivers, and/or multiple antennas.

The wireless device 202 may also include a signal detector 218 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 214. The signal detector 218 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 202 may alsoinclude a digital signal processor (DSP) 220 for use in processingsignals. The DSP 220 may be configured to generate a data unit fortransmission. In some aspects, the data unit may comprise a physicallayer data unit (PPDU). In some aspects, the PPDU is referred to as apacket.

The wireless device 202 may further comprise a user interface 222 insome aspects. The user interface 222 may comprise a keypad, amicrophone, a speaker, and/or a display. The user interface 222 mayinclude any element or component that conveys information to a user ofthe wireless device 202 and/or receives input from the user.

The various components of the wireless device 202 may be coupledtogether by a bus system 226. The bus system 226 may include a data bus,for example, as well as a power bus, a control signal bus, and a statussignal bus in addition to the data bus. Those of skill in the art willappreciate the components of the wireless device 202 may be coupledtogether or accept or provide inputs to each other using some othermechanism.

Although a number of separate components are illustrated in FIG. 2,those of skill in the art will recognize that one or more of thecomponents may be combined or commonly implemented. For example, theprocessor 204 may be used to implement not only the functionalitydescribed above with respect to the processor 204, but also to implementthe functionality described above with respect to the signal detector218 and/or the DSP 220. Further, each of the components illustrated inFIG. 2 may be implemented using a plurality of separate elements.Furthermore the processor 204 may be used to implement any of thecomponents, modules, circuits, or the like described below, or each maybe implemented using a plurality of separate elements.

As discussed above, the wireless device 202 may comprise an AP 104 or anSTA 106, and may be used to transmit and/or receive communications. FIG.3 illustrates various components that may be utilized in the wirelessdevice 202 to transmit wireless communications. The componentsillustrated in FIG. 3 may be used, for example, to transmit OFDMcommunications. In some aspects, the components illustrated in FIG. 3are used to generate and transmit packets to be sent over a bandwidth ofless than or equal to 1.25 MHz, as will be discussed in additionaldetail below. For ease of reference, the wireless device 202 configuredwith the components illustrated in FIG. 3 is hereinafter referred to asa wireless device 302 a.

The wireless device 302 a may comprise a modulator 302 configured tomodulate bits for transmission. For example, the modulator 302 maydetermine a plurality of symbols from bits received from the processor204 (FIG. 2) or the user interface 222 (FIG. 2), for example by mappingbits to a plurality of symbols according to a constellation. The bitsmay correspond to user data or to control information. In some aspects,the bits are received in codewords. In one aspect, the modulator 302comprises a QAM (quadrature amplitude modulation) modulator, for examplea 16-QAM modulator or a 64-QAM modulator. In other aspects, themodulator 302 comprises a binary phase-shift keying (BPSK) modulator ora quadrature phase-shift keying (QPSK) modulator.

The wireless device 302 a may further comprise a transform module 304configured to convert symbols or otherwise modulated bits from themodulator 302 into a time domain. In FIG. 3, the transform module 304 isillustrated as being implemented by an inverse fast Fourier transform(IFFT) module. In some implementations, there may be multiple transformmodules (not shown) that transform units of data of different sizes. Insome implementations, the transform module 304 may be itself configuredto transform units of data of different sizes. For example, thetransform module 304 may be configured with a plurality of modes, andmay use a different number of points to convert the symbols in eachmode. For example, the IFFT may have a mode where 32 points are used toconvert symbols being transmitted over 32 tones (i.e., subcarriers) intoa time domain, and a mode where 64 points are used to convert symbolsbeing transmitted over 64 tones into a time domain. The number of pointsused by the transform module 304 may be referred to as the size of thetransform module 304.

In FIG. 3, the modulator 302 and the transform module 304 areillustrated as being implemented in the DSP 320. In some aspects,however, one or both of the modulator 302 and the transform module 304are implemented in the processor 204 or in another element of thewireless device 302 a (e.g., see describe above with reference to FIG.2).

As discussed above, the DSP 320 may be configured to generate a dataunit for transmission. In some aspects, the modulator 302 and thetransform module 304 may be configured to generate a data unitcomprising a plurality of fields including control information and aplurality of data symbols. The fields including the control informationmay comprise one or more training fields, for example, and one or moresignal (SIG) fields. Each of the training fields may include a knownsequence of values or symbols. Each of the SIG fields may includeinformation about the data unit, for example a description of a lengthor data rate of the data unit.

Returning to the description of FIG. 3, the wireless device 302 a mayfurther comprise a digital to analog converter 306 configured to convertthe output of the transform module into an analog signal. For example,the time-domain output of the transform module 306 may be converted to abaseband OFDM signal by the digital to analog converter 306. The digitalto analog converter 306 may be implemented in the processor 204 or inanother element of the wireless device 202. In some aspects, the digitalto analog converter 306 is implemented in the transceiver 214 (FIG. 2)or in a data transmit processor.

The analog signal may be wirelessly transmitted by the transmitter 310.The analog signal may be further processed before being transmitted bythe transmitter 310, for example by being filtered or by beingupconverted to an intermediate or carrier frequency. In the aspectillustrated in FIG. 3, the transmitter 310 includes a transmit amplifier308. Prior to being transmitted, the analog signal may be amplified bythe transmit amplifier 308. In some aspects, the amplifier 308 comprisesa low noise amplifier (LNA).

The transmitter 310 is configured to transmit one or more packets ordata units in a wireless signal based on the analog signal. The dataunits may be generated using the processor 204 (FIG. 2) and/or the DSP320, for example using the modulator 302 and the transform module 304 asdiscussed above. Data units that may be generated and transmitted asdiscussed above are described in additional detail below with respect toFIGS. 5-18.

FIG. 4 illustrates various components that may be utilized in thewireless device 202 to receive wireless communications. The componentsillustrated in FIG. 4 may be used, for example, to receive OFDMcommunications. In some aspects, the components illustrated in FIG. 4are used to receive data units over a bandwidth of equal to or less than1.25 MHz. For example, the components illustrated in FIG. 4 may be usedto receive data units transmitted by the components discussed above withrespect to FIG. 3. For ease of reference, the wireless device 202configured with the components illustrated in FIG. 4 is hereinafterreferred to as a wireless device 402 b.

The receiver 412 is configured to receive one or more packets or dataunits in a wireless signal. Data units that may be received and decodedor otherwise processed as discussed below are described in additionaldetail with respect to FIGS. 5-18.

In the aspect illustrated in FIG. 4, the receiver 412 includes a receiveamplifier 401. The receive amplifier 401 may be configured to amplifythe wireless signal received by the receiver 412. In some aspects, thereceiver 412 is configured to adjust the gain of the receive amplifier401 using an automatic gain control (AGC) procedure. In some aspects,the automatic gain control uses information in one or more receivedtraining fields, such as a received short training field (STF) forexample, to adjust the gain. Those having ordinary skill in the art willunderstand methods for performing AGC. In some aspects, the amplifier401 comprises an LNA.

The wireless device 402 b may comprise an analog to digital converter410 configured to convert the amplified wireless signal from thereceiver 412 into a digital representation thereof. Further to beingamplified, the wireless signal may be processed before being convertedby the digital to analog converter 410, for example by being filtered orby being downconverted to an intermediate or baseband frequency. Theanalog to digital converter 410 may be implemented in the processor 204(FIG. 2) or in another element of the wireless device 402 b. In someaspects, the analog to digital converter 410 is implemented in thetransceiver 214 (FIG. 2) or in a data receive processor.

The wireless device 402 b may further comprise a transform module 404configured to convert the representation the wireless signal into afrequency spectrum. In FIG. 4, the transform module 404 is illustratedas being implemented by a fast Fourier transform (FFT) module. Asdescribed above with reference to FIG. 3, the transform module 404 maybe configured with a plurality of modes, and may use a different numberof points to convert the signal in each mode. For example, the transformmodule 404 may have a mode where 32 points are used to convert a signalreceived over 32 tones into a frequency spectrum, and a mode where 64points are used to convert a signal received over 64 tones into afrequency spectrum. The number of points used by the transform module404 may be referred to as the size of the transform module 404. In someaspects, the transform module 404 may identify a symbol for each pointthat it uses.

The wireless device 402 b may further comprise a channel estimator andequalizer 405 configured to form an estimate of the channel over whichthe data unit is received, and to remove certain effects of the channelbased on the channel estimate. For example, the channel estimator 405may be configured to approximate a function of the channel, and thechannel equalizer may be configured to apply an inverse of that functionto the data in the frequency spectrum.

In some aspects, the channel estimator and equalizer 405 usesinformation in one or more received training fields, such as a longtraining field (LTF) for example, to estimate the channel. The channelestimate may be formed based on one or more LTFs received at thebeginning of the data unit. This channel estimate may thereafter be usedto equalize data symbols that follow the one or more LTFs. After acertain period of time or after a certain number of data symbols, one ormore additional LTFs may be received in the data unit. The channelestimate may be updated or a new estimate formed using the additionalLTFs. This new or update channel estimate may be used to equalize datasymbols that follow the additional LTFs. In some aspects, the new orupdated channel estimate is used to re-equalize data symbols precedingthe additional LTFs. Those having ordinary skill in the art willunderstand methods for forming a channel estimate.

The wireless device 402 b may further comprise a demodulator 406configured to demodulate the equalized data. For example, thedemodulator 406 may determine a plurality of bits from symbols output bythe transform module 404 and the channel estimator and equalizer 405,for example by reversing a mapping of bits to a symbol in aconstellation. The bits may be processed or evaluated by the processor204 (FIG. 2), or used to display or otherwise output information to theuser interface 222 (FIG. 2). In this way, data and/or information may bedecoded. In some aspects, the bits correspond to codewords. In oneaspect, the demodulator 406 comprises a QAM (quadrature amplitudemodulation) demodulator, for example a 16-QAM demodulator or a 64-QAMdemodulator. In other aspects, the demodulator 406 comprises a binaryphase-shift keying (BPSK) demodulator or a quadrature phase-shift keying(QPSK) demodulator.

In FIG. 4, the transform module 404, the channel estimator and equalizer405, and the demodulator 406 are illustrated as being implemented in aDSP 420. In some aspects, however, one or more of the transform module404, the channel estimator and equalizer 405, and the demodulator 406are implemented in the processor 204 (FIG. 2) or in another element ofthe wireless device 202 (FIG. 2).

As discussed above, the wireless signal received at the receiver 212comprises one or more data units. Using the functions or componentsdescribed above, the data units or data symbols therein may be decodedevaluated or otherwise evaluated or processed. For example, theprocessor 204 (FIG. 2) and/or the DSP 420 may be used to decode datasymbols in the data units using the transform module 404, the channelestimator and equalizer 405, and the demodulator 406.

Data units exchanged by the AP 104 and the STA 106 may include controlinformation or data, as discussed above. At the physical (PHY) layer,these data units may be referred to as physical layer protocol dataunits (PPDUs). In some aspects, a PPDU may be referred to as a packet orphysical layer packet. Each PPDU may comprise a preamble and a payload.The preamble may include training fields and a SIG field. The payloadmay comprise a Media Access Control (MAC) header or data for otherlayers, and/or user data, for example. The payload may be transmittedusing one or more data symbols. The systems, methods, and devices hereinmay utilize data units with training fields whose peak-to-power ratiohas been minimized.

The wireless device 302 a shown in FIG. 3 shows an example of a singletransmit chain to be transmitted over an antenna. In someimplementations, the wireless device 302 a may implement a portion of aMIMO system using multiple antennas to simultaneously transmit data.

FIG. 5 is a functional block diagram of a MIMO system that may beimplemented in wireless devices such as the wireless device 202 of FIG.2 to transmit and receive wireless communications. The MIMO system maymake use of some or all of the components described with reference toFIG. 3. Bits for transmission that are to be received at an output ofthe receiver are provided to an encoder 504. The encoder 504 may apply aforward error correcting (FEC) code on the bit stream. The FEC code maybe a block code, a convolutional code, or the like. The encoded bits areprovided to an interleaving system 505 that distributes the encoded bitsinto N transmit streams.

The interleaving system 505 includes a stream parser 506 that parses aninput bit stream from the encoder 504 to N spatial stream interleavers508 a, 508 b, and 508 n. The stream parser 506 may be provided with thenumber of spatial streams and parse bits on a round-robin basis. Otherparsing functions may also be used. One parsing function that may beused is k_(n)=N_(TX)*k+n (i.e., round-robin with one bit per spatialstream, then on to the next spatial stream where k_(n) is the input bitindex and N_(TX) is the number of transmitters/spatial streams). Anothermore general function f(k,n) might also be used, for example, sendingtwo bits to a spatial stream, then moving on to the next spatial stream.Each interleaver 508 a, 508 b, and 508 n may each thereafter distributebits so that errors may be recovered due to fading or other channelconditions. Hereinafter the interleavers 508 a, 508 b, and 508 n may bereferred to an interleaver 508.

Each transmit stream may then be modulated by a modulator 502 a, 502 b,or 502 n. As described above with reference to FIG. 3, the bits may bemodulated using modulation techniques such as QPSK (Quaternary PhaseShift Keying) modulation, BPSK (mapping one bit at a time), 16-QAM(mapping group of six bits), 64-QAM, and the like. The modulated bitsfor each stream may be provided to transform modules 510 a, 510 b, and510 n. In some implementations, the transform modules 510 a, 510 b, and510 n may perform an inverse discrete time fourier transform (IDFT) toconvert the modulated bits from a frequency domain into a time domain.The transform modules 510 a, 510 b, and 510 n may operate according todifferent modes as described above with reference to FIG. 3. Forexample, the transform modules 510 a, 510 b, and 510 n may be configuredto operate according to a 32 point mode or a 64 point mode. In someimplementations, the modulated bits may be encoded using space timeblock coding (STBC) and spatial mapping may be performed before beingprovided to transform modules 510 a, 510 b, and 510 n. After themodulated bits have been converted into time domain signals for eachspatial stream, the time domain signal may be converted into an analogsignal via converters 512 a, 512 b, and 512 n as described above withreference to FIG. 3. The signals may then be transmitted usingtransmitters 514 a, 514 b, and 514 c and using antennas 516 a, 516 b, or516 n, into a wireless radio space over a desired frequency bandwidth(e.g., 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz, or higher).

In some embodiments, antennas 516 a, 516 b, and 516 n are distinct andspatially separated antennas. In other embodiments, distinct signalsmight be combined into different polarizations off of fewer than Nantennas. An example of this is where spatial rotation or spatialspreading is done, where multiple spatial streams are mapped on a singleantenna. In any case, it should be understood that distinct spatialstreams can be organized in different manners. For example, a transmitantenna might carry data from more than one spatial stream or severaltransmit antennas might carry data from a spatial stream. For example,consider the case of a transmitter with four transmit antennas and twospatial streams. Each spatial stream can be mapped onto two transmitantennas in that case, so two antennas are carrying data from just onespatial stream.

FIG. 6 is a functional block diagram of an exemplary MIMO system thatmay be implemented in wireless devices such as the wireless device 202of FIG. 2 to receive wireless communications. The wireless device 202 bmay be configured to simultaneously receive transmissions from theantennas 516 a, 516 b, and 516 n of FIG. 5. A wireless device 202 breceives signals from the channel at N antennas 518 a, 518 b, and 518 n(counting separate polarizations, as appropriate) coupled to N receivecircuits. The signals are then provided to receivers 620 a, 620 b, and620 n that each may include an amplifier configured to amplify thereceived signals. The signals may then be converted into a digital formvia converters 622 a, 622 b, and 622 n.

Converted signals may then be converted into a frequency spectrum viatransform modules 624 a, 624 b, and 624 n. As described above, thetransform modules 624 a, 624 b, and 624 n may operating according tovarious modes according to the size and bandwidth used (e.g., 32 point64 point, etc.). The transformed signals may be provided to respectivechannel estimator and equalizer blocks 626 a, 626 b, and 626 n that mayfunction similarly as described above with reference to FIG. 4. Afterchannel estimation, the outputs may be provided to a MIMO detector 628which may thereafter provide its output to demodulators 630 a, 630 b,and 630 n which may demodulate the bits according to one of themodulation techniques as described above. Demodulated bits may then beprovided to deinterleavers 632 a, 632 b, and 632 n which may pass bitsinto a stream de-parser 634 which may provide the bits into a single bitstream into a decoder 636 that may decode the bits into an appropriatedata stream.

As described above, data units exchanged by the AP 104 and the STA 106may include control information or data, as discussed above in the formof physical (PHY) layer packets or physical layer protocol data units(PPDUs).

FIG. 7 is a block diagram showing an exemplary structure of a preamble702 and payload 710 of a physical layer packet 700. The preamble 702 mayinclude a short training field (STF) 704 that includes an STF sequenceof known values. In some aspects, the STF may be used for packetdetection (e.g., to detect the start of a packet) and for coarsetime/frequency estimation. The STF sequence may be optimized to have alow PAPR and include a subset of non-zero tones with a particularperiodicity. The STF 704 may span one or multiple OFDM symbols. Thepreamble 702 may further include a long training field (LTF) 706 thatmay span one or multiple OFDM symbols and may include one or more LTFsequences of known non-zero values. The LTF may be used for channelestimation, fine time/frequency estimation, and mode detection. Thepreamble 702 may further include a signal field (SIG) 708 as describedabove that may include a number of bits or values used in one aspect formode detection purposes and determination of transmission parameters.

As described above, certain implementations described herein may bedirected to to wireless communication systems that may be used for smartmetering or in a smart grid network. These wireless communicationsystems may be used to provide sensor applications or be used in homeautomation. Wireless devices used in such systems may instead or inaddition be used in a healthcare context, for example for personalhealthcare. They may also be used for surveillance, to enableextended-range Internet connectivity (e.g., for use with hotspots), orto implement machine-to-machine communications. Accordingly, someimplementations may use low data rates such as approximately 150 KpbsImplementations may further have increased link budget gains (e.g.,around 20 dB) over other wireless communications such as 802.11b. Inaccordance with low data rates, if wireless nodes are configured for usein a home environment, certain aspects may be directed toimplementations with good in-home coverage without power amplification.Furthermore, certain aspects may be directed to single-hop networkingwithout using a MESH protocol. In addition, certain implementations mayresult in significant outdoor coverage improvement with poweramplification over other wireless protocols. Furthermore, certainaspects may be directed to implementations that may accommodate largeoutdoor delay-spread and reduced sensitivity to Doppler. Certainimplementations may achieve similar LO accuracy as traditional WiFi.

Accordingly, certain implementations are directed to transmitting andreceiving wireless signals in sub-gigahertz bands. In one aspect, thismay result in a propagation gain of, for example, 8.5 dB (e.g.,available due to 900 MHz vs. 2.4 GHz). In another aspect, obstructionloss may be reduced by using sub-gigahertz signal which may result in,for example, a 3 dB gain.

Certain implementations are further directed to sending wireless signalswith low bandwidths in sub-gigahertz bands. This may further allowachieving greater link budget gains over other wireless communicationsystems. For example, in one exemplary implementation, a symbol may beconfigured to be transmitted or received using a bandwidth of 1 MHz. Awireless device 202 may be configured to operate in one of severalmodes. In one mode, symbols such as OFDM symbols may be transmitted orreceived using a bandwidth of 1 MHz. In another mode, symbols may betransmitted or received using a bandwidth of 2 MHz. Additional modes mayalso be provided for transmitting or receiving symbols using a bandwidthof 4 MHz, 8 MHz, 16 MHz, and the like. The bandwidth may also bereferred to as the channel width.

Each mode may use a different number of tones/subcarriers fortransmitting the information. For example, in one implementation, a 1MHz mode (corresponding to transmitting or receiving symbols using abandwidth of 1 MHz) may use 32 tones. In one aspect, using a 1 MHz modemay provide for a 13 dB noise reduction as compared to a bandwidth suchas 20 MHz. In addition, low rate techniques may be used to overcomeeffects such as frequency diversity losses due to a lower bandwidthwhich could result in 4-5 dB losses depending on channel conditions. Togenerate/evaluate symbols sent or received using 32 tones, a transformmodule 304 or 404 as described above may be configured to use a 32 pointmode (e.g., a 32 point IFFT or FFT). The 32 tones may be allocated asdata tones, pilot tones, guard tones, and a DC tone. In oneimplementation, 24 tones may be allocated as data tones, 2 tones may beallocated as pilot tones, five tones may be allocated as guard tones,and 1 tone may be reserved for the DC tone. In this implementation, thesymbol duration may be configured to be 40 us including cyclic prefix.

For example, a wireless device 302 a (FIG. 3) may be configured togenerate a packet for transmission via a wireless signal using abandwidth of 1 MHz. In one aspect, the bandwidth may be approximately 1MHz where approximately 1 MHz may be within a range of 0.8 MHz to 1.2MHz. The packet may be formed of one or more OFDM symbols having 32tones allocated as just described using a processor 320. A transformmodule 304 in a transmit chain may be configured as an IFFT moduleoperating according to a thirty-two point mode to convert the packetinto a time domain signal. A transmitter 310 may then be configured totransmit the packet.

Likewise, a wireless device 402 b (FIG. 4) may be configured to receivethe packet over a bandwidth of 1 MHz. In one aspect, the bandwidth maybe approximately 1 MHz where approximately 1 MHz may be within a rangeof 0.8 MHz to 1.2 MHz. The wireless device 402 b may include a processor420 including a transform module 404 in a receive chain that may beconfigured as an FFT module operating according to a thirty-two pointmode to transform the time domain signal into a frequency spectrum. Aprocessor 420 may be configured to evaluate the packet. The 1 MHz modemay support a modulation and coding scheme (MCS) for both a low datarate and a “normal” rate. According to some implementations, thepreamble 702 may be designed for a low rate mode that offers reliabledetection and improved channel estimation as will be further describedbelow. Each mode may be configured to use a corresponding preambleconfigured to optimize transmissions for the mode and desiredcharacteristics as will be further described below.

In addition to a 1 MHz mode, a 2 MHz mode may additionally be availablethat may be used to transmit and receive symbols using 64 tones. In oneimplementation, the 64 tones may be allocated as 52 data tones, 4 pilottones, 1 DC tone, and 7 guard tones. As such, a transform module 304 or404 may be configured to operate according to a 64 point mode whentransmitting or receiving 2 MHz symbols. The symbol duration may also be40 μs including cyclic prefix. Additional modes with differentbandwidths (e.g., 4 MHz, 8 MHz, and 16 MHz) may be provided that may usetransform modules 304 or 404 operating in modes of correspondingdifferent sizes (e.g., 128 point FFT, 256 point FFT, 512 point FFT,etc.). In addition, each of the modes described above may be configuredadditionally according to both a single user mode and a multi user mode.Wireless signals using bandwidths less than or equal to 2 MHz mayprovide various advantages for providing wireless nodes that areconfigured to meet global regulatory constraints over a broad range ofbandwidth, power, and channel limitations.

Additional modes transmitting over different signal bandwidths are alsopossible. For example symbols may be transmitted over bandwidths of 625KHz, 1.25 MHz, or 5 MHz according to some implementations. For example,a wireless device 302 a may be configured to generate a packet fortransmission via a wireless signal using a bandwidth of lower than orequal to 1.25 MHz. In one aspect, the bandwidth may be lower than orequal to approximately 1.25 MHz where approximately 1.25 MHz may bewithin a range of 1.1 MHz to 1.4 MHz. In another aspect, the bandwidthmay be between 625 KHz and 1.25 MHz. The packet may be formed of one ormore OFDM symbols having 32 tones allocated as 24 data tones, 2 pilottones, 5 guard tones, and 1 DC tone using a processor 320. A transformmodule 304 in a transmit chain may be configured as an IFFT moduleoperating according to a thirty-two point mode to convert the packetinto a time domain signal. A transmitter 310 may then be configured totransmit the packet.

Likewise, a wireless device 402 b may be configured to receive thepacket over a bandwidth of lower than or equal to 1.25 MHz. In oneaspect, the bandwidth may be lower than or equal to approximately 1.25MHz where approximately 1.25 MHz may be within a range of 1.1 MHz to 1.4MHz. In another aspect, the bandwidth may be between 625 KHz and 1.25MHz. The wireless device 402 b may include a processor 420 including atransform module 404 in a receive chain that may be configured as an FFTmodule operating according to a thirty-two point mode to transform thetime domain signal into a frequency spectrum. A processor 420 may beconfigured to evaluate the packet using one or more of the componentsdescribed above with reference to FIGS. 2, 4, and 6.

In some aspects, the wireless device 202 is configured to operateaccording to several wireless standards, for example according to one ofthe 802.11 standards. In this configuration, the wireless device 202 mayhave a mode for operating in a 20 MHz channel width in the 2.4 GHz or 5GHz band, as well as a mode for operating in a 40 MHz channel width inthe 2.4 GHz band. In another aspect, the wireless device 202 isconfigured to operate pursuant to the 802.11ac standard. In thisconfiguration, the wireless device 202 has a mode for operating in eachof a 20 MHz, 40 MHz, and 80 MHz channel width. Generally, the transformmodule 304 or 404 may use 64 tones when the wireless device 202 isoperating in the 20 MHz band, may use 128 tones when the wireless device202 is operating in the 40 MHz band, and may use 256 tones when thewireless device 202 is operating in the 80 MHz band.

In some aspects, the controller 224 is configured to adjust operation ofthe wireless device 202 so as to operate in a sub-gigahertz band asdescribed above. In one implementation, to operate according to a modesuch as 1 MHz, 2 MHz, 4 MHz, etc. as described above, a controller 224may be configured to downclock one or more of the components in thewireless device 202 such that the wireless device 202 will operate in a1 MHz, 2 MHz, 4 MHz, 8 MHz, or 16 MHz. In addition, the controller 224may be configured to downclock operation of one or more of thecomponents in the wireless device 202 such that the wireless device 202will operate in modes corresponding to using bandwidths of 5 MHz, 2.5MHz, 1.25 MHz, and/or 0.625 MHz channel width. During such downclockedoperation, the number of tones used by the transform module 304 or 404may remain the same in some aspects.

Downclocking operation of the wireless device 202 may comprise operatingone or more of the components illustrated in FIG. 2 at a reduced clockrate. For example, the downclocking may comprise operating the processor204, the signal detector 218, the DSP 220, and/or any other digitalsignal circuitry at a lower rate, for example by adjusting, modifying,or assigning the timing settings of one or more of these components. Insome aspects, the downclocked operation is performed in response to acommand from the controller 224. In some aspects, the controller 224provides a clock signal which is reduced in comparison to a clock signalused when operating in the 20 MHz, 40 MHz, or 80 MHz channel width.

In some aspects, the controller 224 is configured to cause the operationof the wireless device 202 to be downclocked by a factor of 10 (e.g., by10×). In such configuration, operation in the 20 MHz channel width willbe downclocked to operation in a 2 MHz channel width, and operation inthe 40 MHz channel width will be downclocked to operation in a 4 MHzchannel width. Furthermore, operation in the 80 MHz channel width willbe downclocked to operation in an 8 MHz channel width, and operation inthe 160 MHz channel width will be downclocked to operation in a 16 MHzchannel width.

In some aspects, the controller 224 is configured to cause the operationof the wireless device 202 to be downclocked by a factor of 4 (e.g., by4×). In such configuration, operation in the 20 MHz channel width willbe downclocked to operation in a 5 MHz channel width, and operation inthe 40 MHz channel width will be downclocked to operation in a 10 MHzchannel width.

In some aspects, the controller 224 is configured to cause the operationof the wireless device 202 to be downclocked by a factor of 8 (e.g., by8×). In such configuration, operation in the 20 MHz channel width willbe downclocked to operation in a 2.5 MHz channel width, and operation inthe 40 MHz channel width will be downclocked to operation in a 5 MHzchannel width. Similarly, operation in the 80 MHz channel width will bedownclocked to operation in a 10 MHz channel width.

In some aspects, the controller 224 is configured to cause the operationof the wireless device 202 to be downclocked by a factor of 16 (e.g., by16×). In such configuration, operation in the 20 MHz channel width willbe downclocked to operation in a 1.25 MHz channel width, and operationin the 40 MHz channel width will be downclocked to operation in a 2.5MHz band. Similarly, operation in the 80 MHz channel width will bedownclocked to operation in a 2.5 MHz channel width.

In order to enable operation in a 0.625 MHz channel width, operation inthe 20 MHz channel width may be downclocked by a factor of 32 (e.g., by32×). As discussed above, during such operation, the transform module304 or 404 may continue to operate using 64 tones. When the wirelessdevice 202 operates in the 0.625 MHz channel width, the carrierfrequency will be reduced, which may decrease the phase noise. When thewireless device 202 operates in the 1 MHz mode, downclocking may beused, for example by a factor of 10×, for purposes such as providing thesymbol duration (e.g., for 40 μs.

When operating according to a 0.625 channel width, when the transformmodule 304 and/or the transform module 404 uses 32 points instead of 64,operation in a 20 MHz channel width may be downclocked by 16×.Downclocking by 16× instead of by 32× reduces the increase in symbolduration, which reduces the phase drift within a transmitted symbol. Insuch aspects, any increase in phase noise due to downclocking by 16×instead of 32× may be offset by the reduction in phase drift, which mayreduce hardware requirements. Further, requirements of the pulseposition modulation (PPM) may be eased due to frequency offset in 16×.Similar benefits may also apply to using a 1 MHz bandwidth.

Similarly as described above, in one aspect, when a 1 MHz bandwidth fortransmission or reception of OFDM symbols is used, a 32 point transformmodule 304 or 404 may be used. In this case tones may be allocated as 24data tones, 2 pilot tones, 5 guard tones, and a DC tone. In anotheraspect, when a 2 MHz bandwidth for transmission or reception of OFDMsymbols is used, a 64 point transform module 304 or 404 may be used. Inthis case tones may be allocated as 52 data tones, 4 pilot tones, 7guard tones, and a DC tone. In yet another aspect, when a 4 MHzbandwidth for transmission or reception of OFDM symbols is used, a 64point transform module 304 or 404 may be used. In this case tones may beallocated as 108 data tones, 6 pilot tones, 11 guard tones, and three DCtones. In yet a further aspect, when a 8 MHz bandwidth for transmissionor reception of OFDM symbols is used, a 256 point transform module 304or 404 may be used. In this case tones may be allocated as 234 datatones, 8 pilot tones, 11 guard tones, and three DC tones. Accordingly,the spacing between tones for these bandwidths may be 31.25 KHz. Inaddition, the symbol duration may be 40 μs including a cyclic prefix ofeither 4 μs (for short cyclic prefixes) or 8 μs (for long cyclicprefixes). A longer cyclic prefix may be used to accommodate outdoordelay spreads. Furthermore, large symbol durations may be needed to keepcyclic prefix overhead manageable.

Similar tone allocations may be used for other bandwidths. For example,in another aspect, when a 625 KHz bandwidth for transmission orreception of OFDM symbols is used, a 32 point transform module 304 or404 may be used. In this case tones may be allocated as 24 data tones, 2pilot tones, 5 guard tones, and a DC tone. In another aspect, when a1.25 MHz bandwidth for transmission or reception of OFDM symbols isused, a 64 point transform module 304 or 404 may be used. In this case,tones may be allocated as 52 data tones, 4 pilot tones, 7 guard tones,and a DC tone. In yet another aspect, when a 2.5 MHz bandwidth fortransmission or reception of OFDM symbols is used, a 64 point transformmodule 304 or 404 may be used. In this case tones may be allocated as108 data tones, 6 pilot tones, 11 guard tones, and three DC tones. Inyet a further aspect, when a 5 MHz bandwidth for transmission orreception of OFDM symbols is used, a 256 point transform module 304 or404 may be used. In this case tones may be allocated as 234 data tones,8 pilot tones, 11 guard tones, and three DC tones. Accordingly, thespacing between tones for these bandwidths may be 19.5 KHz. In addition,the symbol duration may be 51.2 μs including a cyclic prefix of either6.4 μs (short) or 12.8 μs (long).

In some aspects, the amount by which operation of the wireless device202 is downclocked is predetermined. For example, the downclockingfactor may be stored in the memory 206 or the controller 224, and loadedat startup of the wireless device 202.

In such configuration, the controller 224 may cause the wireless device202 to operate in a downclocked mode according to the predetermined orloaded downclocking factor.

In some aspects, the amount by which operation of the wireless device202 is downclocked at any given time may be determined in situ. Forexample, the signal detector 218 may determine a downclocking factorfrom a beacon or pilot received by the receiver 212. In some aspects,this factor is determined at startup of the device, or when connectingto the network for the first time. In some aspects, a new factor isdetermined during handoff of the wireless device 202 or each time thewireless device 202 connects to a new network. In some aspects, apredetermined factor may be modified or updated based on a receivedsignal, such as based on a received beacon or pilot. In this way, thewireless device 202 may operate in different bandwidths pursuant to alocation of the device or a network to which the device is connecting,for example. The controller 224 may cause the wireless device 202 tooperate in a downclocked mode according to the determined downclockingfactor.

In some aspects, the wireless device 202 is permanently configured tooperate in the downclocked mode. For example, the components of thewireless device 202 may be hardwired or have firmware installed thereinthat causes the device to always perform downclocked operation. In suchaspects, the wireless device 202 may be incapable of communicating inthe 20 MHz, 40 MHz, and 80 MHz channel widths. Further, the factor ofdownclocking may be fixed in such aspects. For example, the componentsmay be manufactured and/or installed so as to implement only the fixeddownclocking factor. In other aspects, the wireless device may beoperated in any of the 20 MHz, 40 MHz, and 80 MHz channel widths, or maybe selectively downclocked by the controller 224 to operate in the 1MHz, 2 MHz, 4, MHz, 8 MHz, and 16 MHz channel width.

In some implementations, when transmitting in a sub-gigahertz range(e.g., 900 MHz), a repetition mode may be used where repetition codingis implemented. A repetition mode may allow for accurate transmissionover long distances without sacrificing too much preamble overhead. Insome implementations 2× repetition encoding may be used. For example,repetition encoding may allow for as little as 105 dB of pathloss toprovide good in-home coverage. When using a wireless sensor network,without repetition coding, customers may have to install higher-powersensors in difficult to reach places. It may not be practical to selltwo types of sensors (sensors for “easy to reach places” versus“difficult to reach places”). Furthermore, high-power sensors may not beable to work with low power batteries (e.g., coin-cell batteries) due topeak current drain. Alternatively, without repetition, multiple APscould be installed. However, choosing location & configuration of theAPs could be non-trivial for an average consumer. As such, repetitioncoding may provide various advantages for certain implementations forlow data rate applications such as sensor networks.

As an example, in one aspect BPSK rate ½ coding may be used with 4×repetition yielding 94 Kbps. In another aspect, BPSK rate ½ coding maybe used with 2× repetition yielding 188 Kbps. In yet another aspect,BPSK rate ½ coding may be used yielding 375 Kbps. In a further aspect,64 QAM rate ¾ coding may be used resulting in 3.75 Mbps.

In some implementations, the 1 MHz mode and the 2 MHz mode may berequired and configured to be interoperable. Using two required modesmay avoid issues where devices could be configured for some regulatoryregions but may not work for other regulatory regions and may allow fordevices to have more options if regulatory constraints change allowingfor less restrictive communications. Higher bandwidths (e.g., 8 MHz) maybe used for cellular offload.

With reference to FIG. 7, when transmitting packets in sub-gigahertzbands with bandwidths as described above, the preamble 702 may bedesigned to have robust mode detection in an early state of the preambleto detect between different modes. The preamble 702 may further beoptimized to minimize overhead and provide adequate coexistence ofdevices transmitting using the 1 MHz mode and devices transmitting usinggreater than or equal to 2 MHz modes. The preamble 702 may be designedto have robust mode detection in an early state of the preamble todetect between 1 MHz transmissions (32 pt FFT) and 2 MHz transmissions(64 pt FFT). The physical layer packet 700 may be generated fortransmission for different data rates to allow in one aspect fortransmission of data over greater distances. For example, the physicallayer packet 700 may be generated for a low data rate along with another“normal” data rate as described above.

FIG. 8A is a block diagram showing an exemplary structure of a preamble802 a and payload 810 a of a physical layer packet 800 a fortransmission over a bandwidth of substantially 1 MHz according tocertain implementations. The physical layer packet 800 a may begenerated using a transform module 304 (FIG. 3) that is configuredaccording to a 32 point FFT mode for transmitting an OFDM symbol with 32tones as described above.

The preamble 802 a may include a short training field (STF) 804 a. TheSTF 804 a may include a sequence of known values with a subset ofnon-zero values corresponding to a subset of non-zero tones with aparticularly chosen periodicity. The periodicity of the non-zero tonesmay be the same as used for STF sequences used in higher bandwidths suchas 2 MHz. In some implementations, the STF field 804 a may be boosted,such as by 3 dB for repetition coding. The STF 804 a may be sent overfour OFDM symbols where each symbol repeats a known STF sequence.

The preamble 802 a may further include a long training field (LTF) 806a. The LTF 806 a may be formed of four OFDM symbols and may include anLTF sequence transmitted in each symbol. The LTF sequences may be formedof known non-zero values corresponding to non-zero tones for all pilotand data tones. In some implementations, the LTF sequences may thereforeinclude 26 non-zero values.

The preamble 802 a may further include a signaling field (SIG) 808 a. Insome exemplary implementations, the SIG field 808 a may be repetitioncoded. In some implementations, the SIG field 808 a may be 2× repetitioncoded. The physical layer packet 800 a may further include the payload810 a that may be generated using 24 tones in each OFDM symbol allocatedfor data. The preamble 802 a may be used for generating either a lowrate or a normal rate 1 MHz transmission. The preamble 802 a may be usedaccording to a single user mode.

As described above, the SIG field 808 a for a 1 MHz mode may be twosymbols. In one implementation, the entries into the SIG field 808 a maycorrespond to the entries shown in Table 1 below. As such, the SIG field808 a may include 36 bits. The SIG field 808 a may be coded at BPSK-rate½ repetition 2×.

TABLE 1 Field Bits Description Space Time 1 May indicate whether SpaceTime Block Coding Block Coding is used Number of 2 Spatial Streams ShortGuard 1 Interval Coding 2 1^(st) bit may be coding type (LDPC/BCC) while2^(nd) bit may be for LDPC N_(sym) ambiguity Modulation 4 Coding Scheme(MCS) Aggregation Bit 1 Signals use of AMPDU Length 9 My be in symbolswhen aggregation is on or in bytes when aggregation is off. An AMPDU maybe required for packet sizes greater than 511 bytes Reserved 6 May beused for MAC bits CRC 4 Tail 6 May be needed for BCC but could be lessbits

FIG. 8B is a block diagram showing an exemplary structure of a preamble802 b and payload 810 b of a physical layer packet 800 b fortransmission over a bandwidth of substantially 2 MHz according to asingle user mode. The physical layer packet 800 b may be generated usinga transform module 304 (FIG. 3) that is configured according to a 64point FFT mode for transmitting an OFDM symbol with 64 tones asdescribed above.

The preamble 802 b may include a short training field (STF) 804 b. TheSTF 804 b may include a sequence of known values with a subset ofnon-zero values corresponding to a subset of non-zero tones over 64tones with a determined periodicity. The periodicity of the non-zerotones may be the same as used for STF sequences used for 1 MHztransmissions. The preamble 802 b may further include a long trainingfield (LTF) 806 b. The LTF 806 b may be formed of two OFDM symbols andmay include LTF sequences transmitted in each symbol. The LTF sequencesmay comprise non-zero values corresponding to non-zero tones for allpilot and data tones. The LTF sequences may therefore include 56non-zero values in some implementations. The preamble 802 b may furtherinclude a signaling field (SIG) 808 b. The SIG field 808 b may be formedfrom two OFDM symbols. The two OFDM symbols of the SIG field 808 b mayeach be QBPSK rotated. If more than one spatial streams are being used,the preamble 802 b may include additional long training fields (LTFs)816 b for each of the additional spatial streams being used (e.g., asthe LTF 804 b may correspond to the first spatial stream if there aremore than one). The physical layer packet 800 b may further include thepayload 810 b that may be generated using 52 tones in each OFDM symbolallocated for data. The preamble 802 b may be used according to a singleuser mode.

FIG. 8C is a block diagram showing an exemplary structure of a preamble802 c and payload 810 c of a physical layer packet 800 c fortransmission over a bandwidth of 2 MHz according to a multi user mode.As described above with reference to FIG. 8B, the physical layer packet800 c may be generated using a transform module 304 (FIG. 3) that isconfigured according to a 64 point FFT mode for transmitting an OFDMsymbol with 64 tones.

The preamble 802 c may include a short training field (STF) 804 c. TheSTF 804 c may include a sequence of known values with a subset ofnon-zero values corresponding to a subset of non-zero tones over 64tones with a determined periodicity. The periodicity of the non-zerotones may be the same as used for STF sequences used for 1 MHztransmissions. The preamble 802 c may further include a long trainingfield (LTF) 806 c. The LTF 806 c may be formed of two OFDM symbols andmay include LTF sequences transmitted in each symbol. The LTF sequencesmay comprise non-zero values corresponding to non-zero tones for allpilot and data tones. The LTF sequences may therefore include 56non-zero values according to some implementations. The preamble 802 cmay further include a signaling field (SIG) 808 c. The SIG field 808 cmay be formed from two OFDM symbols. The first of the two OFDM symbolsof the SIG field 808 c may be QBPSK rotated. In one aspect, this allowsfor the receiver to detect whether the packet 800 c is multi-user modepacket or a single user mode packet based on whether only one of the SIGfield symbols is QBPSK rotated. The preamble 802 c may further include avery high throughput short training field (VHT-STF) 814 c. The VHT-STF814 c may correspond to a VHT-STF used for IEEE 802.11ac transmissions.The preamble 802 c may further include one or more very high throughputlong training fields (VHT-LTFs) 816 c corresponding to each spatialstream being used. The VHT-LTFs 816 c may correspond to VHT-LTFs usedfor IEEE 802.11ac transmissions. The preamble 802 c may further includea very high throughput signal field (VHT-SIG-B) 818 c. The VHT-SIG-B 818c may correspond to the VHT-SIG-B used for IEEE 802.11ac transmissions.The physical layer packet 800 c may further include the payload 810 cthat may be generated using 52 tones in each OFDM symbol allocated fordata. The preamble 802 c may be used according to a multi user mode.

Differentiating between a 32 point mode (i.e., 1 MHz) and a 64 pointmode (2 MHz) may be done by using an LTF sequence that is orthogonal infrequency across 32 and 64 tone mode, or by detecting the QBPSK rotationon the 1^(st) SIG symbol.

As described above, a wireless device 202 may be configured to generateOFDM symbols for transmission over bandwidths greater than 2 MHz, suchas for 4 MHz, 8 MHz, 16 MHz, and 32 MHz. In some implementations, whensending OFDM symbols over bandwidths greater than 2 MHz, the SIG field806 b (FIG. 8B) may be duplicated in every 2 MHz segment of the OFDMsymbol and may be used to be able to determine the bandwidth of thesymbol. As the OFDM symbol for the SIG field may use 52 tones allocatedfor data, duplication of the SIG field may leave 7 guard tones (3 and 4tones on the ends of the symbol) for higher bandwidths (4 MHz, 8 MHz, 16MHz).

In some cases, it may be desirable to use additional guard tones for theLTF 806 b and/or SIG 808 b fields. For example, it may be desirable forthe 4 MHz, 8 MHz, and 16 MHz preamble symbols to correspond tocorresponding symbols used for 40 MHz, 80 MHz, and 160 MHz of 802.11actransmissions. As one example, the LTF 806 b may use the VHT-LTFs for 40MHz, 80 MHz, and 160 MHz 802.11ac transmissions depending on whether theOFDM symbol is for 4 MHz, 8 MHz, and 16 MHz respectively. As theVHT-LTFs for 40 MHz, 80 MHz, and 160 MHz have 11 guard tones (⅚), usingthese VHT-LTFs may not provide non-zero values for channel estimationfor 2 tones at each edge, for example if the SIG 808 b field allocated52 tones for data. Furthermore, there may be stricter filteringrequirements for symbols being transmitted using greater bandwidths (4MHz, 8 MHz, and 16 MHz) if the LTF 806 b and SIG 808 b are transmittedusing 52 data tones (i.e., having less guard tones). Duplicating the LTF802 b used for 2 MHz transmissions may fail to adequately address theseissues as the LTF uses 52 non-zero tones and thus the same guard toneissue remains. As such, an optimized LTF 806 b and SIG 808 b may beprovided for 2, 4, and 8 MHz transmissions. In one aspect, the fieldsare chosen so as to be able to re-use 20, 40, and 80 MHz LTF sequencesused for IEEE 802.11ac packets.

As such, in one implementation, for the 2 MHz packets shown in FIGS. 8Band 8C, the SIG fields 808 b and 808 c may be transmitted using adifferent tone allocation than the rest of the fields of the packets 800b and 800 c. For example, The SIG fields 808 b and 808 c may betransmitted using 48 data tones rather than 52 data tones. This maycorrespond to the tone allocation used for an L-SIG of 802.11a toneallocation. This SIG field 808 b and 808 c may then be duplicated foreach 2 MHz segment for transmissions over 2 MHz. In anotherimplementation, the STFs 804 b and 804 c, the LTFs 806 b and 806 c, andthe SIG fields 808 b and 808 c may be generated for transmission using adifferent tone allocation than the rest of the fields of the packet. Forexample the STFs 804 b and 804 c, the LTFs 806 b and 806 c, and the SIGfields 808 b and 808 c may be generated for transmission using 48 tonesallocated for data.

As described above, the SIG fields 808 b and 808 c for a 2 MHz mode mayuse two symbols transmitting up to 52 bits of data. The entries into theSIG fields 808 b and 808 c may correspond to the entries shown in Table2 below. The first 26 bits in Table 2 may correspond to the first symbolwhile the last 26 bits in Table 2 may correspond to the second symbol.It should be appreciated that while 52 bits of data are shown in thetable below, as described above, in some implementations, the SIG fields808 b and 808 c may be sent using 48 data tones and as such the SIGfield may correspond to 48 bits. In one corresponding implementation,the number of reserved bits shown in Table 2 below may be reduced sothat 48 bits are sent or received.

TABLE 2 Field Bits Description Bandwidth 2 This may indicate a bandwidthmode (e.g., 2 MHz, 4 MHz, 8 MHz, or 16 MHz) Reserved 1 Space Time Block1 Indicates whether Space Time Block Coding Coding is used Nsts/GID/AID14 For Single User (SU) Mode — 2 bits may indicate Nsts, 0-12 bits mayindicate partial AID For Multi User (MU) Mode — 8 bits may indicateNsts, 6 bit GID Reserved 1 Short Guard Interval 1 (SGI) Coding 2 1^(st)bit may indicate a coding type for SU (or for user zero for MU) while2^(nd) bit may be used for LDPC Nsym ambiguity Modulation Coding 4 ForMU mode, the first 3 bits may indicate Scheme (MCS) coding type forusers 1-3 while the last is reserved) Beamformed 1 May indicate to thereceiverf a beamforming steering matrix is applied to the waveform in aSU mode Aggregation Bit 1 Reserved for MU Length 9 Length field (insymhois when aggregation is on and in bytes when aggregation is off) Maymandate AMPDU for packet sizes > 511 bytes and for MU Reserved 4 Dopplerbit may be indicated here Midamble/Doppler 1 CRC 4 Tail 6 May be neededfor BCC

FIG. 9 is a block diagram showing another exemplary structure of apreamble 910 and payload 920 of a physical layer packet 900 fortransmission via wireless signal. The packet 900 may be used when thewireless device 202 is downclocked from the 20 MHZ channel width or the40 MHz channel width to operate in a 1.25 MHz or 2.5 MHz channel width,respectively.

In the illustrated aspect, the packet 900 comprises a preamble 910 and apayload 920. The preamble 910 may include a training field and signal(SIG) field. In the aspect illustrated in FIG. 9, the training fieldcomprises a short training field (STF) 912 followed by a long trainingfield (LTF) 914. Each of the STF 912 and LTF 914 may comprise 2 symbols.

The preamble 910 further comprises a SIG field 916. The SIG field 916may indicate a duration of the packet 900, as well as other parameterssuch as bandwidth of a remaining portion of the packet 900. In someaspects, the SIG field 916 comprises a space-time block coding (STBC)sub-field, a modulation and coding scheme (MCS) sub-field, and/or acyclic redundancy check (CRC) sub-field. As illustrated in FIG. 9, theSIG field 916 may comprise 2-3 symbols. In some aspects, the SIG field916 comprises a greater number of symbols.

In some aspects, the SIG field 916 is transmitted in the lowestbandwidth being used in the wireless system 100 or being used by the AP104, or is transmitted to be compatible with a transform module usingthe lowest number of points in the wireless system 100. For example,when 1.25 MHz and 2.5 MHz channel widths are being transmitted over 64and 128 tones, respectively, the SIG field 916 is transmitted over 64tones. This may similarly be applied for channel widths of 1 MHz and 2MHz respectfully. This allows terminals that are incapable of receivingcommunications over the higher bandwidth or over a greater number oftones, or terminals that are not listening on the higher bandwidth orover the greater number of tones, to receive the SIG field 916 anddetermine the length of the packet 900. In this way, collisions in thesystem 100 may be reduced because all terminals, regardless of thebandwidth or transform module they are using, may determine when thepacket 900 is being communicated. The STF 912 and/or the LTF 914 may betransmitted in the same channel width or over the same number of tonesas the SIG field 916. A remaining portion of the packet 900 may betransmitted in the same bandwidth or in a different bandwidth, or overthe same or a different number of tones, which may be indicated in theSIG field 916.

The STF 912 and the LTF 914 may comprise a high throughput shorttraining field sequence (HT-STF) and an HT-LTF, respectively that maycorrespond to fields used according to an IEEE 802.11n transmission. Inthe preamble 910, however, the length of the SIG field 916 may begreater than the length of the HT-SIG field in the Greenfield preamble.This increased length may be used to indicate transmission featureswhich are not available in the 802.11n standard.

For example, in addition to being used when the wireless device 202 isdownclocked to operate in a 1.25 MHz or 2.5 MHz channel width, thepacket 900 may additionally be used when the wireless device 202 isdownclocked from the 80 MHz channel width to operate in a 5 MHz channelwidth. In this aspect, the SIG field 916 may include an additionalsymbol so that the SIG field 916 may indicate whether a 1.25 MHz, 2.5MHz, or 5 MHz channel width is used for a remaining portion of thepacket 900.

In some aspects, the length of the STBC sub-field, MCS sub-field, or CRCsub-field may be reduced in comparison to the 802.11n Greenfieldpreamble. For example, instead of including a number of bits in the STBCsub-field sufficient to allow for an odd number of space-time streams,the STBC sub-field may be reduced to one bit in some aspects. In suchaspect, the bit indicates whether STBC encoding was performed withrespect to all of the space-time streams or alternatively none of thespace-time streams. When the length of the STBC sub-field, MCSsub-field, and/or CRC sub-field is reduced, the SIG field 916 mayinclude bits that indicate whether a 1.25 MHz, 2.5 MHz, or 5 MHz channelwidth is used for a remaining portion of the packet 900 withoutincreasing the length of the SIG field 916 in comparison to the 802.11nGreenfield preamble (and similarly for a 1 MHz, 2 MHz, or 4 MHz channelwidth). In one aspect, the MCS sub-field may have a length of less than7 bits while the CRC sub-field may have a length of less than 8 bits. Asshown in Tables 1 and 2, the MCS sub-field may have a length of 4 bitswhile the CRC may also have a length of 4 bits.

In some aspects, the SIG field 916 may comprise an indicator signifyingwhether multi-user multiple input multiple output (MU-MIMO) informationis included. In these aspects, some or all of the MU-MIMO informationmay be transmitted in the SIG field 916. Thus, the increased length ofthe SIG field 916 may be used to include such indicator and/or suchMU-MIMO information.

In some aspects, the SIG field 916 is transmitted and received over 52data tones. In contrast, the HT-SIG field is typically sent over 48 datatones when transmitting pursuant to 802.11n in order to accommodatelegacy terminals. Further, the SIG field 916 may be transmitted withoutrotation in some aspects, in contrast to 802.11n Greenfieldtransmission.

The packet 900 may further comprise one or more data or extension LTFs918. The data or extension LTFs 918 may be used to form a channelestimate for demodulating the payload 920. In aspects where MU-MIMOinformation is included in the SIG field 916, the number of data orextensions LTF 918 may be based at least in part on the number of usersfor which the MU-MIMO information is included. Further, the packet 900may include one or more additional STFs after the SIG field 918 when theMU-MIMO information is included. The one or more additional STFs may besteer or beamformed, for example by using different precoding.

When the system 100 is using 1.25 MHz, 2.5 MHz, and 5 MHz channelwidths, or when the wireless device 202 is configured to receive ortransmit communications over all three of these bandwidths, a preamblethat is similar to the preamble used in 802.11ac communications may beused by the wireless device 202. As discussed above, a 20 MHz, 40 MHz,or 80 MHz channel width may be used with 802.11ac communications. Thus,a downclocked version of the 802.11ac preamble may be used when channelwidths of 1.25 MHz, 2.5 MHz, and 5 MHz are being used.

In some aspects, the L-SIG field which is generally included in the802.11ac preamble may be omitted in the downclocked preamble. Omittingthe L-SIG field may reduce the length of the preamble in some aspects.

FIG. 10 illustrates an example of a packet 1000 in which an L-SIG fieldis omitted. The packet 1000 may comprise a PHY layer packet for use withthe wireless device 202. The packet 1000 may be used when the wirelessdevice 202 is downclocked from the 20 MHZ, 40 MHz, and 80 MHz channelwidths to operate in 1.25 MHz, 2.5 MHz, and 5 MHz channel widths,respectively.

The packet 1000 comprises a preamble 1010 and a payload 1030. Thepreamble 1010 comprises an STF 1012, and LTF 1014, and a SIGA field1016. In some aspects, the STF 1012, LTF 1014, and SIGA field 1016 mayinclude information similar to the information included in the STF 912,LTF 914, and SIG field 916, respectively.

In one aspect, an L-SIG field that could be included between the LTF1014 and the SIGA field 1016 in other implementations is omitted. Insome aspects, the length of the SIGA field 1016 is less than the lengthof the combined length of the L-SIG field and the SIGA field in the802.11ac standard. In some aspects, the SIGA field 1016 indicates aduration of the packet 1000 and/or indicates whether MU-MIMO informationis included. The SIGA field 1016 may further indicate which of the 1.25MHz, 2.5 MHz, and 5 MHz channel widths is used for a remaining portionof the packet 1000 (or similarly 1 MHz, 2 MHz, and 4 MHz).

The preamble 1010 may further comprise one or more STFs 1022 and one ormore LTFs 1024. The STFs 1022 and LTFs 1024 may include informationsimilar to the information included in the LTFs 918 and the additionalSTFs discussed above with respect to FIG. 9. The preamble 1010 mayfurther comprise one or more SIGB fields 1026. The SIGB fields 1026 mayinclude user-specific information such as modulation and coding rate.

In some aspects, the portions of the packet 1000 that are shaded in FIG.10 are spatially multiplexed, beamformed, or otherwise steered to adifferent device, for example when MU-MIMO is used. Each of the STFs1022, LTFs 1024, and/or SIGB fields 1026 may include informationspecific to a user or device when MU-MIMO is used.

FIG. 11 illustrates an example of a packet 1100. The packet 1100 maycomprise a PHY layer packet for use with the wireless device 202, forexample. The packet 1100 may be used in the system 100 when the 0.625MHz channel width is enabled.

The packet 1100 comprises a preamble 1110 and a payload 1120. Thepreamble 1110 comprises an STF 1112, an LTF 1114, and a SIG field 1116.The STF 1112 and the LTF 1114 each comprise two symbols, and may includeinformation similar to the information included in the STF 912 and theLTF 914, respectively.

In contrast to the STF 912 and the LTF 914, however, both of the STF1112 and the LTF 1114 are compatible with a transform module using 32points. For example, the wireless device 202 may generate the STF 1112and the LTF 1114 by using the 32-point mode of the transform module 304when generating the packet 1100 for transmission. Similarly, thewireless device 202 may use the 32-point mode of the transform module404 to evaluate the STF 1112 and the LTF 1114 when the packet 1100 isreceived.

In some aspects, the STF 1112 and the LTF 1114 are optimized to have alow peak-to-average power ratio (PAPR) over 32 tones. The STF 1112 andLTF 1114 may be repeated across frequencies when transmitted overbandwidths greater than 0.625 MHz.

In the aspect illustrated in FIG. 11, the SIG field 1116 comprises 3-6symbols. In some aspects, the SIG field 916 comprises a greater numberof symbols. Further, the SIG field 1116 is compatible with a transformmodule using 32 points.

The SIG field 1116 may include all of the information which the SIGfield 916, discussed above with respect to FIG. 9, includes. Forexample, the SIG field 1116 may indicate a duration of the packet 1100,as well as other parameters. The SIG field 1116 may comprise an STBCsub-field, an MCS sub-field, and/or a CRC sub-field. The SIG field 1116may further include information regarding MU-MIMO, and may indicatewhether a 0.625 MHz, 1.25 MHz, 2.5 MHz, or 5 MHz channel band is usedfor a remaining portion of the packet 1100 (or similarly 1 MHz, 2 MHz, 4MHz, or 8 MHz).

The SIG field 1116 may be transmitted over 32 tones, however, due to thecompatibility with the transform using 32 points. Thus, the length ofthe SIG field 1116 is greater than the length of the SIG field 916 inorder to accommodate all of the information that may be contained in theSIG field 1116. In some aspects, the length of the SIG field 1116 isdouble the length of the SIG field 916 when similar information isincluded in the two. In some aspects, the SIG field 1116 may have fewerthan twice the number of symbols in the SIG field 916 when transmittedsimilar information. For example, although the SIG field 914 maycomprise 2 symbols in certain aspects, the SIG field 1116 may consist ofonly 3 symbols when transmitting the same information. This may beaccomplished in some aspects by reducing the number of bits in the STBC,MCS, and/or CRC sub-fields.

In some aspects, the length of the SIG field 1116 varies based on itscontents. The SIG field 1116 may be repeated across frequencies whentransmitted over bandwidths greater than 0.625 MHz.

The preamble 1110 may further comprise one or more data or extensionLTFs 1118. The data or extension LTFs 1118 may be configured similar tothe LTFs 918, and the payload 1120 may be configured similar to thepayload 920, except that each of the LTFs 1118 and the payload 1120 maybe transmitted or received in the 0.625 MHz channel width. Thus, each ofthe each of the LTFs 1118 and the payload 1120 may be operated on by atransform module using 32 points, and each may be received over 24-32tones.

In some aspects, it may be possible to reduce the length of the SIGfield 1116 by dividing the SIG field 1116 into a plurality of portions.For example, FIG. 12 illustrates an example of a packet 1200 having adivided SIG field. The packet 1200 may comprise a PHY layer packet foruse with the wireless device 202, and may be used in the system 100 whenthe 0.625 MHz channel width is enabled.

The packet 1200 comprises a preamble 1210 and the payload 1220,discussed above with respect to FIG. 11. The preamble 1210 comprises theSTF 1212 and the LTF 1214 discussed above.

The preamble 1210 further comprises a SIG1 field 1216 a and a SIG2 field1216 b. In some aspects, a great number of SIG fields may be included inthe packet 1200. In the aspect illustrated in FIG. 12, the SIG1 field1216 a comprises one symbol, and the SIG2 field 1216 b comprises 2-3symbols. In some aspects, either of the SIG1 field 1216 a and the SIG2field 1216 b may comprise additional symbols.

In the packet 1200, a SIG1 field 1216 a is compatible with a transformmodule having the smallest size in the wireless system 100. In thewireless system 100 discussed above, the smallest size transform moduleuses 32 points (e.g., when transmitting or receiving in the 0.625 MHzchannel width). As can be seen in FIG. 12, the SIG1 field 1216 a iscompatible with a transform module using 32 tones, and thus may betransmitted and received over 32 tones. The SIG1 field 1216 a may berepeated across frequencies when transmitted over bandwidths greaterthan 0.625 MHz.

The SIG1 field 1216 a may indicate a duration of the packet 1200. Thus,all terminals in the wireless system 100, regardless of the bandwidth ortransform module they are using, may determine when the packet 1200 isbeing communicated. Further, the SIG1 field 1216 a indicates a number oftones or a transform module size for receiving the SIG2 field 1216 b, ora bandwidth over which the SIG2 field 1216 b is transmitted. Forexample, the SIG1 field 1216 a may indicate whether the SIG2 field 1216b should be evaluated with a transform module using 32 points or 64points, and/or whether the SIG2 field 1216 b should be received over the0.625 MHz channel width, or over a 1.25 MHz, 2.5 MHz, or 5 MHz channelwidth.

In some aspects, a higher bandwidth is used for the SIG2 field 1216 bthan is used for the SIG1 field 1216 a. The higher bandwidth may be usedwhen transmitting to terminals that are configured for reception in thehigher bandwidth, or based on a bandwidth allocation determined by theAP 106. In some aspects, the amount of information being conveyed in theSIG2 field 1216 b may be used to determine which bandwidth is used forthe SIG2 field 1216 b.

When the SIG2 field 1216 b is transmitted in a greater bandwidth, forexample over a greater number of tones, than the SIG1 field 1216 a, moreinformation may be included in the SIG2 field 1216 b than may fit in theSIG1 field 1216 a. Bifurcating the SIG field of the packet 1200 asdiscussed herein may therefore ensure that the duration of the packet1200 may be properly determined by all terminals in the system 100,while reducing the length of the SIG field (i.e., the combined length ofthe SIG1 field 1216 a and SIG2 field 1216 b) in certain communications.For example, the SIG2 field 1216 b may be transmitted over 64 tones forbandwidths greater than 0.625 MHz, which may reduce the 3-6 symbollength of the SIG field 1116 illustrated in FIG. 11. Such transmissionmay in some aspects reduce the combined length of the SIG1 field 1216 aand SIG2 field 1216 b to two totals symbols.

The packets and functionality described above with reference to FIGS.9-12 may be likewise applied to channel widths of 1 MHz, 2 MHz, 4 MHz,and 8 MHz (e.g., where 0.625 MHz may correspond to 1 MHz, 1.25 MHz maycorrespond to 2 MHz, and so on).

As described above, in some aspects, it may be desirable to use apreamble and/or packet format suitable for a transmission rate that islower than the rate exhibited when using one of the packets 800-1200described above. In such aspects, a downclocked version of the preambleused in the 802.11b standard may be implemented. In these aspects, 32×downclocking may be performed to enable a 0.625 MHz channel width, and16× downclocking may be performed to enable a 1.25 MHz channel width,for use with direct-sequence spread spectrum (DSSS) communications. Inone aspect, the shorter preamble defined in the 802.11b standard isdownclocked for use with the DSSS communications. Although the shorterpreamble defined in 802.11b is typically associated with a rate of 2Mbps and the longer preamble defined in 802.11b is typically associatedwith a rate of 1 Mbps, in some aspects the wireless device 202implements a downclocked 802.11b short preamble which is associated withrates at least as low as 1 Mbps scaled by the factor that is used toperform the downclocking.

FIG. 13 illustrates an aspect of a method 1300 for generating andtransmitting a packet. The method 1300 may be used to generate any ofthe packets described above. The packets may be generated at either theAP 104 or the STA 106 and transmitted to another node in the wirelessnetwork 100. Although the method 1300 is described below with respect toelements of the wireless device 202, those having ordinary skill in theart will appreciate that other components may be used to implement oneor more of the steps described herein.

At block 1302, a packet is generated for wireless transmission. In theaspect illustrated in FIG. 13, the packet includes at least one trainingfield and information indicating a duration of the packet. Thegeneration may be performed by the processor 204 and/or the DSP 220, forexample using the modulator 302 and the transform module 304. Operationof one or more of these components may be downclocked by the controller224 during the generation. The training field may comprise an STF and/orand LTF. The information may be included in a SIG field of the packet.

Next, at block 1304, a wireless signal including the packet istransmitted. In the aspect illustrated in FIG. 13, at least a portion ofthe wireless signal is transmitted over a bandwidth lower than or equalto approximately 2.5 MHz. The transmission may be performed by thetransmitter 210, for example. Further, operation of the transmitter 210may in some aspects be controlled at least in part by the controller224. The portion may be transmitted over 32 tones in some aspects. Theportion may correspond to a SIG field of the packet or to a firstportion of a bifurcated SIG field.

FIG. 14 illustrates an aspect of a method 1400 for receiving andprocessing a packet. The method 1400 may be used to receive any of thepackets described above. The packets may be received at either the AP104 or the STA 106 from another node in the wireless network 100.Although the method 1400 is described below with respect to elements ofthe wireless device 202, those having ordinary skill in the art willappreciate that other components may be used to implement one or more ofthe steps described herein.

At block 1402, a wireless signal including a packet is received. In theaspect illustrated in FIG. 10, the packet includes at least one trainingfield. In this aspect, at least a portion of the wireless signal isreceived over a bandwidth lower than or equal to approximately 2.5 MHz.The reception may be performed by the receiver 212, for example.Further, operation of the receiver 212 may in some aspects be controlledat least in part by the controller 224. In some aspects, the bandwidthis 1.25 MHz or is 0.625 MHz. The training field may comprise an STFand/or and LTF. The portion may be received over 32 tones in someaspects. The portion may correspond to a SIG field of the packet or to afirst portion of a bifurcated SIG field.

Thereafter, at block 1404, a duration of the packet is determined basedat least in part on the portion of the wireless signal. Thedetermination may be performed by the processor 204, the signal detector218, and/or the DSP 220, for example using the transform module 404 andthe demodulator 406. Operation of one or more of these components may bedownclocked by the controller 224 during the determination. The durationmay be determined based on an indicator in the SIG field or a portionthereof.

FIG. 15 is a flow chart of another exemplary method 1500 for receivingand evaluating a packet sent via a wireless signal. The method 1500 maybe used to receive any of the packets described above. The packets maybe received at either the AP 104 or the STA 106 from another node in thewireless network 100. Although the method 1500 is described below withrespect to elements of the wireless device 202, those having ordinaryskill in the art will appreciate that other components may be used toimplement one or more of the steps described herein.

At block 1502, a wireless signal including a packet is received. Atleast a portion of the wireless signal is received over a bandwidthlower than or equal to 1.25 MHz. In one aspect, the bandwidth may belower than or equal to approximately 1.25 MHz where approximately 1.25MHz may be within a range of 1.1 MHz to 1.4 MHz. In some implementationsthe wireless signal is received over a bandwidth equal to 1 MHz. In oneaspect, the bandwidth may be equal to approximately 1 MHz whereapproximately 1 MHz may be within a range of 0.8 MHz to 1.2 MHz. Thereception may be performed by the receiver 212, for example. Further,operation of the receiver 212 may in some aspects be controlled at leastin part by the controller 224. The packet is formed from at least oneorthogonal frequency-division multiplexing (OFDM) symbol comprisingthirty-two tones, the thirty-two tones corresponding to frequencysubcarriers within the bandwidth. The thirty-two tones of the at leastone OFDM symbol are allocated as: twenty-four data tones, two pilottones, five guard tones, and one direct current (DC) tone.

At block 1504, the wireless signal is evaluated where evaluatingincludes converting the at least one OFDM symbol into a frequency domainsignal using a thirty-two point mode. The wireless signal may beevaluated at a processor 220. The processor 220 may include a transformmodule 404 configured to perform the conversion into the frequencydomain using a thirty-two point mode. The evaluation may be performed bythe processor 204, the signal detector 218, and/or the DSP 220, forexample using the transform module 404 and the demodulator 406.Operation of one or more of these components may be downclocked by thecontroller 224 during the evaluation.

FIG. 16 is a flow chart of another exemplary method 1600 for generatingand transmitting a packet via a wireless signal. The packets may begenerated at either the AP 104 or the STA 106 and transmitted to anothernode in the wireless network 100. Although the method 1600 is describedbelow with respect to elements of the wireless device 202, those havingordinary skill in the art will appreciate that other components may beused to implement one or more of the steps described herein.

At block 1602, a packet is generated for transmission via a wirelesssignal. The packet is generated for transmission using at least oneorthogonal frequency-division multiplexing (OFDM) symbol comprisingthirty-two tones, the thirty-two tones corresponding to frequencysubcarriers. The thirty-two tones of the at least one OFDM symbol areallocated as: twenty-four data tones, two pilot tones, five guard tones,and one direct current (DC) tone. The generation may be performed by theprocessor 204 and/or the DSP 220, for example using the modulator 302and the transform module 304. Operation of one or more of thesecomponents may be downclocked by the controller 224 during thegeneration.

Next, at block 1604, at least one OFDM symbol is converted into a timedomain signal using a thirty-two point mode. A transform module 304 maybe configured to operate according the thirty-two point mode to performthe conversion. At block 1606, the packet is transmitted via thewireless signal over a bandwidth that is lower than or equal to 1.25MHz. In one aspect, the bandwidth may be lower than or equal toapproximately 1.25 MHz where approximately 1.25 MHz may be within arange of 1.1 MHz to 1.4 MHz. In one implementation, the packet istransmitted via the wireless signal over a bandwidth that is equal toapproximately 1 MHz. In one aspect, the bandwidth may be equal toapproximately 1 MHz where approximately 1 MHz may be within a range of0.8 MHz to 1.2 MHz. The transmission may be performed by the transmitter210, for example. Further, operation of the transmitter 210 may in someaspects be controlled at least in part by the controller 224.

FIG. 17 is a functional block diagram of yet another exemplary wirelessdevice 1700 that may be employed within the wireless communicationsystem 100. Those skilled in the art will appreciate that a wirelesscommunication device 1700 may have more components than the wirelesscommunication devices shown in FIGS. 2-6. The device 1700 comprises areceiving module 1702 for wirelessly receiving data. The receivingmodule 1702 may be configured to perform one or more of the functionsdiscussed above with respect to the block 1502 illustrated in FIG. 15.The receiving module 1702 may correspond to the receiver 212, and mayinclude the amplifier 401. In some cases, a means for receiving mayinclude the receiving module 1702. The device 1700 further comprises adecoding module 1704 for evaluating a wireless signal. The decodingmodule 1704 may be configured to perform one or more of the functionsdiscussed above with respect to the block 1504 illustrated in FIG. 15.In some cases a means for evaluating may include the decoding module1704.

FIG. 18 is a functional block diagram of another exemplary wirelessdevice 1800 that may be employed within the wireless communicationsystem 100. Those skilled in the art will appreciate that a wirelesscommunication device 1800 may have more components than the wirelesscommunication devices shown in FIGS. 2-6. The wireless communicationdevice 1800 shown includes only those components useful for describingsome prominent features of certain implementations. The device 1800includes a generating module 1802 for encoding data for wirelesstransmission. In some cases a means for generating may include thegenerating module 1802. The generating module 1802 may be configured toperform one or more of the functions described above with respect toblock 1602 of FIG. 16. The device 1800 may further comprise a transformmodule 1804 for converting a signal into a time domain. In some cases, ameans for converting may include the transform module 1806. Thetransform module 1804 may be configured to perform one or more of thefunctions described above with respect to block 1604 of FIG. 16. Thedevice 1800 further comprises a transmitting module 1806 for wirelesslytransmitting the output from the generating module 1802. Thetransmitting module 1806 may be configured to perform one or more of thefunctions discussed above with respect to the block 1606 illustrated inFIG. 16. The transmitting module 1806 may correspond to the transmitter210. In some cases, a means for transmitting may include thetransmitting module 1806. The transmitting module 1806 may include avariety of components including, but not limited to, a constellationmapper, a modulator, an IDFT (inverse discrete time fourier transformmodule or IFFT 304 as described above with reference to FIG. 3), adigital to analog converter, an amplifier, an antenna, and othercomponents.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like. Further, a “channel width” as used herein may encompass ormay also be referred to as a bandwidth in certain aspects.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for wireless communication, comprising:receiving a wireless signal comprising a packet, at least a portion ofthe wireless signal being received over a bandwidth, wherein the packetis formed from at least one orthogonal frequency-division multiplexing(OFDM) symbol; and evaluating the wireless signal, the evaluatingcomprising converting the at least one OFDM symbol into a frequencydomain signal; and wherein converting the at least one OFDM symbolcomprises down-clocking operation of a processor by a factor of greaterthan or equal to 8; and wherein the packet comprises a preamble portionand a payload portion, and wherein the preamble portion of the packetcomprises at least one of a short training field (STF), a long trainingfield (LTF), and a signal (SIG) field; and wherein the short trainingfield (STF) comprises four or fewer OFDM symbols, and wherein the longtraining field (LTF) comprises four OFDM symbols.
 2. The method of claim1, wherein the SIG field comprises at least one of a space-time blockcoding (STBC) sub-field having a length of 1 bit, a modulation andcoding scheme (MCS) sub-field having a length of less than 7 bits, and acyclic redundancy check (CRC) sub-field having a length of less than 8bits.
 3. The method of claim 2, wherein the MCS sub-field has a lengthof 4 bits, and wherein the CRC sub-field has a length of 4 bits.
 4. Themethod of claim 1, wherein the SIG field is repetition encoded.
 5. Themethod of claim 4, wherein the SIG field is two times repetitionencoded.
 6. The method of claim 1, wherein the at least a portion of thewireless signal is received over a bandwidth equal to 1 MHz.
 7. Anapparatus for wireless communication, comprising: a receiver configuredto receive a wireless signal comprising a packet, at least a portion ofthe wireless signal being configured to be received over a bandwidth,wherein the packet is formed from at least one orthogonalfrequency-division multiplexing (OFDM) symbol; and a processorconfigured to evaluate the wireless signal, the processor comprising atransform circuit configured to covert the at least one OFDM symbol intoa frequency domain signal, wherein evaluating the at least one OFDMsymbol comprises down-clocking operation of the processor by a factor ofgreater than or equal to 8, wherein the packet comprises a preambleportion and a payload portion, and wherein the preamble portion of thepacket comprises at least one of a short training field (STF), a longtraining field (LTF), and a signal (SIG) field, and wherein the shorttraining field (STF) comprises four or fewer OFDM symbols, and whereinthe long training field (LTF) comprises four OFDM symbols.
 8. Theapparatus of claim 7, wherein the SIG field comprises at least one of aspace-time block coding (STBC) sub-field having a length of 1 bit, amodulation and coding scheme (MCS) sub-field having a length of lessthan 7 bits, and a cyclic redundancy check (CRC) sub-field having alength of less than 8 bits.
 9. The apparatus of claim 8, wherein the MCSsub-field has a length of 4 bits, and wherein the CRC sub-field has alength of 4 bits.
 10. The apparatus of claim 7, wherein the SIG field isrepetition encoded.
 11. The apparatus of claim 10, wherein the SIG fieldis two times repetition encoded.
 12. The apparatus of claim 7, whereinthe at least a portion of the wireless signal is configured to bereceived over a bandwidth equal to 1 MHz.
 13. A method for wirelesscommunication, comprising: generating a packet for transmission via awireless signal, wherein the packet is generated for transmission usingat least one orthogonal frequency-division multiplexing (OFDM) symbol,wherein generating the at least one OFDM symbol comprises down-clockingoperation of a processor by a factor of greater than or equal to 8; andtransmitting the packet via the wireless signal over a bandwidth,wherein the packet comprises a preamble portion and a payload portion,and wherein the preamble portion of the packet comprises at least one ofa short training field (STF), a long training field (LTF), and a signal(SIG) field; and wherein the short training field (STF) comprises fouror fewer OFDM symbols, and wherein the long training field (LTF)comprises four OFDM symbols.
 14. The method of claim 13, wherein the SIGfield comprises at least one of a space-time block coding (STBC)sub-field having a length of 1 bit, a modulation and coding scheme (MCS)sub-field having a length of less than 7 bits, and a cyclic redundancycheck (CRC) sub-field having a length of less than 8 bits.
 15. Themethod of claim 14, wherein the MCS sub-field has a length of 4 bits,and wherein the CRC sub-field has a length of 4 bits.
 16. The method ofclaim 13, wherein the SIG field is repetition encoded.
 17. The method ofclaim 16, wherein the SIG field is two times repetition encoded.
 18. Themethod of claim 13, wherein the at least a portion of the wirelesssignal is transmitted over a bandwidth equal to 1 MHz.
 19. An apparatusfor wireless communication, comprising: a processor configured togenerate a packet for transmission via a wireless signal, wherein thepacket is generated for transmission using at least one orthogonalfrequency-division multiplexing (OFDM) symbol, wherein the processor isconfigured to down-clock operation of the processor by a factor ofgreater than or equal to 8; a transmitter configured to transmit thepacket via the wireless signal over a bandwidth, wherein the packetcomprises a preamble portion and a payload portion, and wherein thepreamble portion of the packet comprises at least one of a shorttraining field (STF), a long training field (LTF), and a signal (SIG)field; and wherein the short training field (STF) comprises four orfewer OFDM symbols, and wherein the long training field (LTF) comprisesfour OFDM symbols.
 20. The apparatus of claim 19, wherein the SIG fieldcomprises at least one of a space-time block coding (STBC) sub-fieldhaving a length of 1 bit, a modulation and coding scheme (MCS) sub-fieldhaving a length of less than 7 bits, and a cyclic redundancy check (CRC)sub-field having a length of less than 8 bits.
 21. The apparatus ofclaim 20, wherein the MCS sub-field has a length of 4 bits, and whereinthe CRC sub-field has a length of 4 bits.
 22. The apparatus of claim 19,wherein the SIG field is repetition encoded.
 23. The apparatus of claim22, wherein the SIG field is two times repetition encoded.
 24. Theapparatus of claim 19, wherein the at least a portion of the wirelesssignal is configured to be transmitted over a bandwidth equal to 1 MHz.25. The method of claim 1, wherein: the bandwidth is between 0.625 MHzand 1.25 MHz; and the at least one OFDM symbol comprises thirty-twotones, the thirty-two tones corresponding to frequency subcarrierswithin the bandwidth, and wherein the thirty-two tones of the at leastone OFDM symbol are allocated as: twenty-four data tones, two pilottones, five guard tones, and one direct current (DC) tone.
 26. Theapparatus of claim 7, wherein: the bandwidth is between 0.625 MHz and1.25 MHz; and the at least one OFDM symbol comprises thirty-two tones,the thirty-two tones corresponding to frequency subcarriers within thebandwidth, and wherein the thirty-two tones of the at least one OFDMsymbol are allocated as: twenty-four data tones, two pilot tones, fiveguard tones, and one direct current (DC) tone.
 27. The method of claim13, wherein: the bandwidth is between 0.625 MHz and 1.25 MHz; and the atleast one OFDM symbol comprises thirty-two tones, the thirty-two tonescorresponding to frequency subcarriers within the bandwidth, and whereinthe thirty-two tones of the at least one OFDM symbol are allocated as:twenty-four data tones, two pilot tones, five guard tones, and onedirect current (DC) tone.
 28. The apparatus of claim 19, wherein: thebandwidth is between 0.625 MHz and 1.25 MHz; and the at least one OFDMsymbol comprises thirty-two tones, the thirty-two tones corresponding tofrequency subcarriers within the bandwidth, and wherein the thirty-twotones of the at least one OFDM symbol are allocated as: twenty-four datatones, two pilot tones, five guard tones, and one direct current (DC)tone.